Semiconductor device and method for forming the same

ABSTRACT

A semiconductor structure includes a semiconductor substrate, a gate structure, a source/drain structure, a contact, a dielectric layer, and a metal line. The gate structure is on the semiconductor substrate. The source/drain structure is adjacent to the gate structure. The contact lands on the source/drain structure. The dielectric layer spas the contact and the gate structure. The metal line extends through the dielectric layer to the contact. The metal line includes a liner over the contact, a magnetic layer over the liner, a graphene layer over the magnetic layer, and a filling metal over the graphene layer. The magnetic layer has a greater permeability coefficient than the filling metal.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a Divisional Application of the U.S.application Ser. No. 17/313,379, filed on May 6, 2021, which claimspriority to U.S. Provisional Application Ser. No. 63/142,536, filed Jan.28, 2021, all of which are herein incorporated by reference in theirentirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs. Each generation has smaller and more complexcircuits than the previous generation.

In the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometric size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling-downprocess generally provides benefits by increasing production efficiencyand lowering associated costs.

However, these advances have increased the complexity of processing andmanufacturing ICs. Since feature sizes continue to decrease, fabricationprocesses continue to become more difficult to perform. Therefore, it isa challenge to form reliable semiconductor devices at smaller andsmaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flowchart of a method for forming a semiconductor device inaccordance with some embodiments of the present disclosure.

FIGS. 2 to 9 illustrate a method in various stages of forming a graphenelayer in accordance with some embodiments of the present disclosure.

FIG. 10A is a schematic diagram of a deposition system in accordancewith some embodiments of the present disclosure.

FIG. 10B illustrates a mechanism related to functioning of thedeposition system in accordance with some embodiments of the presentdisclosure.

FIG. 11A illustrates experimental results showing different operationtime durations of an RF (radio frequency) source effect on temperaturesof a magnetic layer.

FIG. 11B illustrates a partial enlarged view of FIG. 11A.

FIGS. 12A to 12C illustrate experimental results of a Raman spectrum ofgraphene formed over a magnetic layer with different operation timedurations of the RF (radio frequency) source.

FIG. 13 illustrates experimental results showing different operationtime durations of the RF (radio frequency) source effect on ratios of dband to g band (d/g ratio) of graphene formed over a magnetic layer.

FIG. 14 illustrates experimental results showing different operationtime durations of the RF (radio frequency) source effect on electricalproperties.

FIGS. 15 to 32 illustrate a method in various stages of forming asemiconductor device in accordance with some embodiments of the presentdisclosure.

FIG. 33 illustrates a semiconductor device in accordance with someembodiments of the present disclosure.

FIGS. 34 and 35 illustrate schematic transmission electron microscopyimages showing different graphene growth experimental results formed indifferent deposition time durations.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, “around,” “about,” “approximately,” or “substantially”may generally mean within 20 percent, or within 10 percent, or within 5percent of a given value or range. Numerical quantities given herein areapproximate, meaning that the term “around,” “about,” “approximately,”or “substantially” can be inferred if not expressly stated.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

In order to improve the conductivity of a multi-layer interconnect (MLI)of integrated circuit (IC) structure, a graphene layer may be formed ona metal line/via in the MLI by using a chemical vapor deposition (CVD)method. However, forming the graphene layer on the metal line/via byusing the CVD method may require a lengthy deposition time becauseheating rate in the CVD method is too slow to reach a target temperaturefor graphene growth in a short time.

Therefore, the present disclosure in various embodiments provides amethod for forming a graphene layer on a magnetic layer by using adeposition system with an RF source. An advantage is that a shorteneddeposition time for forming the graphene layer may be achieved toimprove the production efficiency, quality, and sheet resistance of thegraphene layer. In greater detail, the magnetic layer can be heated to atarget temperature for graphene growth within few seconds by the RFsource of the deposition system of the present disclosure, which in turnshortens the duration of depositing the graphene layer on the magneticlayer.

Referring now to FIG. 1 , illustrated is a flowchart of an exemplarymethod M for fabrication of a semiconductor device in accordance withsome embodiments. The method M includes a relevant part of the entiremanufacturing process. It is understood that additional operations maybe provided before, during, and after the operations shown by FIG. 1 ,and some of the operations described below can be replaced or eliminatedfor additional embodiments of the method. The order of theoperations/processes may be interchangeable. The method M includesfabrication of a semiconductor device. However, the fabrication of thesemiconductor device is merely an example for describing themanufacturing process according to some embodiments of the presentdisclosure.

FIGS. 2-9 illustrate the method M in various stages of forming agraphene layer in accordance with some embodiments of the presentdisclosure. The method M begins at block S101. Referring to FIG. 2 , insome embodiments of block S101, a magnetic layer is formed over asubstrate, and then a first cleaning process is performed to themagnetic layer. A substrate W1 is shown in FIG. 2 . In some embodiments,the substrate W1 may include a semiconductor substrate, such as a bulksemiconductor, a semiconductor-on-insulator (SOI) substrate, or thelike. An SOI substrate includes a layer of a semiconductor materialformed on an insulator layer. The insulator layer may be, for example, aburied oxide (BOX) layer, a silicon oxide layer, or the like. Theinsulator layer is provided on a substrate, a silicon or glasssubstrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the substrate W1 may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GalnAs,GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, thesubstrate W1 may be undoped or doped (e.g., p-type, n-type, or acombination thereof). Other materials, such as germanium, quartz,sapphire, and glass could alternatively be used for the substrate W1.

As shown in FIG. 2 , a magnetic layer ML1 is deposited over thesubstrate W1. In some embodiments, the magnetic layer ML1 may be amagnetic foil or a magnetic film. In some embodiments, the magneticlayer ML1 may be made of a high permeability coefficient material inorder to enhance the induced Eddy current thereon during the depositionprocess of the graphene layer as shown in FIG. 8 . In other words, themagnetic layer ML1 may be made of a material that has a higherpermeability coefficient than the surrounding layers. By way of examplebut not limiting the present disclosure, the magnetic layer ML1 may havea permeability coefficient greater than about 5×10⁻⁵ (H/m). The term“permeability” as used herein refers to the increase of magnetizationthat occurs when a magnetic material is subjected to an applied magneticfield. In some embodiments, the magnetic layer ML1 may be made of a highhysteresis coefficient material in order to enhance the induced Eddycurrent thereon during the deposition process of the graphene layer GLas shown in FIG. 8 . In other words, the magnetic layer ML1 may be madeof a material that has a higher hysteresis coefficient than thesurrounding layers. By way of example but not limiting the presentdisclosure, the magnetic layer ML1 may have a hysteresis coefficientgreater than about 300 (A/m). In some embodiments, the magnetic layerML1 may be made of a low conductivity material. In other words, themagnetic layer ML1 may be made of a material that has a lowerconductivity coefficient than the surrounding layers. By way of examplebut not limiting the present disclosure, the magnetic layer ML1 may havea conductivity coefficient lower than about 1×10⁷ (S/m).

In some embodiments, the magnetic layer ML1 may be made of a magneticmaterial, such as iron (Fe), cobalt (Co), nickel (Ni), proper alloys,suitable materials, or combinations thereof. By way of example but notlimiting the present disclosure, the magnetic material may be made ofCoPt, CoPd, FePt, or FePd. In some embodiments, the magnetic material inthe magnetic layer ML1 has an atomic percentage greater than or equal toabout 10% (e.g., about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%).In some embodiments, the magnetic material is evenly dispersed in themagnetic layer ML1. That is, any position in the magnetic layer ML1substantially has the same atomic percentage of the magnetic material.In some embodiments, the magnetic material in an upper portion of themagnetic material has a higher atomic percentage than a lower portion ofthe magnetic layer ML1. In some embodiments, an entirety of the magneticlayer ML1 is made of the same magnetic material.

In some embodiments, the magnetic layer ML1 may include a plurality ofmagnetic materials. By way of example but not limiting the presentdisclosure, the plurality of magnetic materials may include iron (Fe),cobalt (Co), nickel (Ni), proper alloys, or other suitable materials,such as CoFeTa, NiFe, CoFe, NiCo. By way of example but not limiting thepresent disclosure, the magnetic layer ML1 may include nickel with anatomic percentage in a range from about 70% to about 90% and iron withan atomic percentage in a range from about 10% to about 30%. By way ofexample but not limiting the present disclosure, the magnetic layer ML1may include nickel with an atomic percentage in a range from about 30%to about 50%, zinc with an atomic percentage in a range from about 10%to about 30% and copper with an atomic percentage in a range from about10% to about 30% plus ferric oxide (e.g., Fe₂O₄) with an atomicpercentage in a range from about 0.5% to about 10%. By way of examplebut not limiting the present disclosure, the magnetic layer ML1 mayinclude yttrium with an atomic percentage in a range from about 70% toabout 90% and bismuth with an atomic percentage in a range from about10% to about 30% plus ferric oxide (e.g., Fe₅O₁₂) with an atomicpercentage in a range from about 0.5% to about 10%. By way of examplebut not limiting the present disclosure, the magnetic layer ML1 mayinclude cobalt with an atomic percentage in a range from about 85% toabout 95%, zirconium with an atomic percentage in a range from about2.5% to about 7.5% and tantalum with an atomic percentage in a rangefrom about 2.5% to about 7.5%.

In some embodiments, the magnetic layer ML1 may be made of nitride orsilicide of a magnetic material, such as nitride or silicide of iron(Fe), cobalt (Co), nickel (Ni), proper alloys thereof, suitablematerials, or combinations thereof. In some embodiments, the magneticlayer ML1 may be made of a ferromagnetic material. By way of example butnot limiting the present disclosure, the magnetic layer ML1 may includean alloy of a rare earth metal and a transition metal (RE-TM alloy),such as terbium iron cobalt (TbFeCo), terbium cobalt (TbCo), RE-cobaltpalladium (RE-CoPd), RE-cobalt platinum (RE-CoPt), suitable materials,or combinations thereof. In some embodiments, the magnetic layer ML1 maybe made of a magnetic material with a dopant, such as boron (B),therein. By way of example but not limiting the present disclosure, themagnetic layer ML1 may be made of CoFeB.

In some embodiments, the magnetic layer ML1 can be deposited on thesubstrate W1 using suitable processes, such as PVD, CVD, ALD,sputtering, electroplating, or the like. In some embodiments, themagnetic layer ML1 has a thickness in a range from about 10 nm to about100 nm. In some embodiments, because the magnetic layer ML1 is exposedto the air, a metal oxide layer MOX may therefore be formed over themagnetic layer ML1 due to oxidation. The metal oxide layer MOX is anoxide of the magnetic layer ML1. For example, if the magnetic layer ML1is made of cobalt (Co), the metal oxide layer MOX may be Cobalt oxide(CoO).

As shown in FIG. 2 , a first cleaning process C1 is performed to cleanthe surface of the substrate W1. In greater detail, the first cleaningprocess C1 is used to remove some contaminants on the metal oxide layerMOX. In some embodiments, the cleaning solvent of the first cleaningprocess C1 is an organic solvent. The organic solvent may have a polarfunction, such as —OH, —COOH, —CO—, —O—, —COOR, —CN—, —SO—, asnon-limiting examples. In various embodiments, the organic solvent mayinclude PGME, PGEE, GBL, CHN, EL, Methanol, Ethanol, Propanol,n-Butanol, Acetone, DMF, Acetonitrile, IPA, THF, Acetic acid, orcombinations thereof.

Referring back to FIG. 1 , the method M then proceeds to block S102where a second cleaning process is performed to remove a metal oxidelayer on the magnetic layer. With reference to FIG. 3 , in someembodiments of block S102, a second cleaning process C2 is performed toremove the metal oxide layer MOX from the magnetic layer ML1. After thesecond cleaning process C2, a top surface of the magnetic layer ML1 isexposed. In some embodiments, the cleaning solvent of the secondcleaning process C2 may be a mineral acid (e.g., inorganic acid), suchas hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO₃),sulfuric acid (H₂SO₄), or the like. In some embodiments where a magneticlayer ML1 is cleaned by a 5% nitride acid, the duration of the secondcleaning process C2 is in a range from about 2 seconds to about 4seconds (e.g., about 3 seconds in some embodiments). If the duration ofthe second cleaning process C2 is too short, the metal oxide layer MOXmay not be sufficiently removed. While if the duration of the secondcleaning process C2 is too long, the cleaning solvent of the secondcleaning process C2 may cause unwanted etch to the magnetic layer ML1.

With continued reference to FIG. 1 , the method M then proceeds to blockS103 where a third cleaning process is performed to remove a residue ofthe second cleaning process from the magnetic layer. With reference toFIG. 4 , in some embodiments of block S103, a third cleaning process C3is performed to remove a residue of the cleaning solvent of the secondcleaning process C2. In some embodiments, the third cleaning process C3may use deionized water (DI water) to remove the cleaning solvent (e.g.,mineral acid) of the second cleaning process C2.

Referring back to FIG. 1 , the method M then proceeds to block S104where the substrate is moved into a processing chamber of a depositionsystem. This is described in greater detail with reference to FIGS. 10Aand 10B, which illustrate a schematic diagram of an exemplary depositionsystem 10 a in some embodiments of the present disclosure. As shown inFIGS. 10A and 10B, the deposition system 10 a includes a processingchamber 100, a gas delivery system 200, an RF system 300, a residue gasanalysis system 400, and a pumping system 500. In some embodiments, thegas delivery system 200 is connected to the processing chamber 100 via agas delivery line G1, and the residue gas analysis system 400 and thepumping system 500 are connected to the processing chamber 100 via a gasdelivery line G2. The RF system 300 is coupled to the processing chamber100 by a coil 110 wound around the exterior of the processing chamber100.

In some embodiments of FIGS. 10A and 10B, the processing chamber 100 isan elongated tube extending laterally. By way of example but notlimiting the present disclosure, the processing chamber 100 may be aquartz tube. In some embodiments, the gas delivery lines G1 and G2 arefluidly communicated with the processing chamber 100, in which the gasdelivery lines G1 and G2 are fluidly communicated with opposite sides ofthe processing chamber 100. The coil 110 is wound around the processingchamber 100 from a top to a bottom of the processing chamber 100. Theprocessing chamber 100 can accommodate a wafer W2. For example, thewafer W2 may include a semiconductor substrate, such as a bulksemiconductor, a semiconductor-on-insulator (SOI) substrate, or thelike. An SOI substrate includes a layer of a semiconductor materialformed on an insulator layer. The insulator layer may be, for example, aburied oxide (BOX) layer, a silicon oxide layer, or the like. Theinsulator layer is provided on a substrate, a silicon or glasssubstrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the wafer W2 may include silicon; germanium; a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, and/or indium antimonide;an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GalnAs,GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, thesubstrate W2 may be undoped or doped (e.g., p-type, n-type, or acombination thereof). Other materials, such as germanium, quartz,sapphire, and glass could alternatively be used for the substrate W2. Amagnetic layer ML2 can be deposited on the wafer W2. In someembodiments, the magnetic layer ML2 can act as a catalytic layer forgrowing a graphene layer, which will be discussed below. In someembodiments, the magnetic layer ML2 as shown in FIG. 10A may besubstantially the same as or comparable to that of the magnetic layerML1 as shown in FIG. 2 . Reference may be made to the detaileddescription provided in the foregoing paragraphs, and a descriptionthereof will not be repeated. The magnetic layer ML2 can be deposited onthe substrate W2 using suitable processes, such as PVD, CVD, ALD,sputtering, electroplating, or the like.

In some embodiments, the inductive coil 110 is connected to the RFsystem 300 through a transmission line such as a wave guide or aco-axial cable. The coil 110 may be made of copper (Cu), or othersuitable conductive materials. In some embodiments, the coil 110 has amultiple turn cylindrical configuration and may have an electricallength of about one-quarter wavelength (<λ/4) at the operatingfrequency. For example, the coil 110 is positioned outside theprocessing chamber 100 for coupling the RF magnetic fields MF into theprocessing chamber 100. These induced RF magnetic fields MF ionize atleast part of the process gases and thus form plasma in processingchamber 100.

The gas delivery system 200 will now be described. In some embodiments,the gas delivery system 200 includes several sources 202, 204, and 206.In the example shown in FIG. 10A, three sources are illustrated, whilemore or less sources may be applied in some other embodiments. The gasdelivery system 200 includes several mass flow controllers 212, 214,216, in which the mass flow controllers 212, 214, 216 are connected tothe sources 202, 204, and 206 via valves V12, V14, V16, respectively.Moreover, the mass flow controllers 212, 214, 216 are connected to thegas delivery line G1 via valves V22, V24, V26, respectively.

In some embodiments, the source 202 is a liquid source, and thus thesource 202 may include a liquid tank. For example, the liquid of thesource 202 may be liquid aromatic hydrocarbon, such as benzene (C₆H₆) ortoluene (C₇H₈). In some embodiments, the carbon elements of the liquidaromatic hydrocarbon (e.g., benzene or toluene) are used as a source fordepositing a graphene layer discussed below.

On the other hand, the sources 204 and 206 are gas sources, and thus thesources 204 and 206 may include gas cylinders. The gases of the sources204 and 206 may be, for example, Hz, Ar, N₂, Cl₂, or other suitablegases.

The RF system 300 will now be described. The RF system 300 includes anRF source 302, a matching box 304, a controller 306, an isolator 308,and a remote control module 310. In some embodiments, the RF energy issupplied to the processing chamber 100 by the inductive coil 110 whichis powered by the RF source 302 and the matching box 304.

The input of the matching box 304 is coupled to the RF source 302, whichprovides RF power for plasma generation. The matching box 304 is used tomatch the impedance of the coil 110 to the impedance of the RF source302, in order to deliver the maximum power to the plasma in theprocessing chamber 100. In some embodiments, the matching box 304includes a matching network, a Phase and Magnitude Detector (PMD) and acontroller that automatically tunes the matching network using theinformation supplied by the PMD.

The controller 306 may control the operation of the RF source 302. Thecontroller 306 may include, for example, a computer including a centralprocessing unit (CPU), a memory, and support circuits. The controller306 operates under the control of a computer program stored in thememory or through other computer programs, such as programs stored in aremovable memory. The computer program dictates, for example, thetiming, mixture of gases, RF power levels and other parameters of aparticular process.

The remote control module 310 is electrically coupled between thecontroller 306 and the RF source 302. In some embodiments, the remotecontrol module 310 enables the controller 306 to operate the RF source302 remotely.

The isolator 308 is electrically coupled to the RF source 302, theremote control module 310, and the controller 306. Generally, theisolator 308 is used to isolate the RF source 302 from the remotecontrol module 310. The isolator 308 is used to protect high-power RFenergy from the RF source 302. If the RF source 302 is connecteddirectly to a load (such as the coil 110), and the load is not wellmatched with the RF source 302, some power reaching the load will bereflected back to the remote control module 310 and then the controller306 that could destroy the controller 306. The isolator 308 between thecontroller 306 and the RF source 302 will absorb most of the reflectedRF energy, which in turn will protect the controller 306 from beingdestroyed.

The residue gas analysis system 400 will now be described. The residuegas analysis system 400 includes a residue gas analyzer (RGA) 402, amain pump 404, and a backing vacuum pump 406. The RGA 402 is connectedto the gas delivery line G2 via a valve V4. In some embodiments, the RGA402 is a spectrometer that effectively measures the chemical compositionof a gas present in a low-pressure environment. For example, the RGA 402can ionize separate components of the gas to create various ions, andthen detects and determines the mass-to-charge ratios. This processworks better in vacuum, where quality is easier to monitor andimpurities and inconsistencies are easier to detect because of the lowpressure.

The main pump 404 is connected to the RGA 402, and the backing vacuumpump 406 is connected to the main pump 404. In some embodiments, thepumps 404 and 406 are connected in series so as to improve the pumpingspeed of the RGA 402. The backing vacuum pump 406 is used to lowerpressure from one pressure state (typically atmospheric pressure) to alower pressure state, after which the main pump 404 is used to evacuatethe process chamber down to high-vacuum levels needed for processing. Insome embodiments, the main pump 404 may be a turbo pump, a cryo pump, anion pump, a diffusion pump, or the like. The backing vacuum pump 406 maybe a rotary vane pump, a scroll pump, or the like. The gas exhaustedfrom the backing vacuum pump may be discharged into a gas handlingsystem (not shown) of a fab via a gas conduit.

The pumping system 500 will now be described. In some embodiments, thepumping system 500 includes a pressure gauge 502, a foreline trap 504,and a vacuum pump 506. The foreline trap 504 in connected to the gasdelivery line G2 via a valve V5. The remainder of the gas mixtureexhausted from the processing chamber 100, including reaction productsor byproducts, is evacuated from the processing chamber 100 by thevacuum pump 506. In some embodiments, the foreline trap 504 may be aparticle collector or a particle filter, which is positioned downstreamfrom the exhaust gas source (e.g., processing chamber 100). In someembodiments, the foreline trap 504 is positioned as close as possible tothe processing chamber 100 in order to maximize the amount of powder andother particulate matter that is collected within the processing chamber100 and minimize the amount that is deposited within other areas of thegas delivery line G2. In some other embodiments, the foreline trap 504may be a cooling trap, which recycles process gases by removingcondensable material from the process gases when flowing through theforeline trap 504.

With reference to FIG. 5 , in some embodiments of block S104, after thethird cleaning process C3, the substrate W1 is loaded into theprocessing chamber 100 of the deposition system. In some embodiments,the gas delivery system 200 of the deposition system 10 d in FIG. 5 onlyincludes two sources 202 and 204. For example, the source 202 is aliquid source, and thus the source 202 may include a liquid tank. Theliquid of the source 202 may, for example, be liquid aromatichydrocarbon, such as benzene (C₆H₆) or toluene (C₇H₈). In someembodiments, the carbon elements of the liquid aromatic hydrocarbon(e.g, Benzene or Toluene) are used as a source for depositing a graphenelayer discussed below. On the other hand, the source 204 is a gassource, and thus the source 204 may include gas cylinder. In someembodiments, the gas of the source 204 may be H₂. In some embodiments, agas delivery line G12 connects the source 202 to the gas delivery lineG1 (or the processing chamber 100), and a gas delivery line G14 connectsthe source 204 to the gas delivery line G1 (or the processing chamber100).

Referring back to FIG. 1 , the method M then proceeds to block S105where a fourth cleaning process is performed to the magnetic layer inthe processing chamber of the deposition system. With reference to FIG.6 , in some embodiments of block S105, a fourth cleaning process C4 isperformed to clean the substrate W1. The fourth cleaning process C4 isperformed by, for example, turning on the valves 14 and 24 of the gasdelivery system 200, such that the gas inside the source 204 can flowthrough the mass flow controller 214 and then flows into the gasdelivery lines G14 and G1. For example, H₂ flows from the source 204into the processing chamber 100 through the gas delivery lines G14 andG1. In some embodiments, the mass flow controller 214 is controlled suchthat the flow rate of H₂ is in a range from about 1 sccm to about 5sccm.

Meanwhile, the RF source 302 of the RF system 300 is turned on with anRF power in a range from about 150 W to about 200 W, such that the H₂that flows into the processing chamber 100 becomes hydrogen plasma (H₂plasma). The hydrogen plasma may etch and clean the magnetic layer ML1over the substrate W1. The plasma can remove unwanted metal oxide on thesubstrate W1. For example, H⁺+CoO→Co+H₂O, in which a reduction-oxidationprocess takes place, such that the CoO becomes Co. In some embodiments,the duration of the fourth cleaning process C4 is in a range from about20 seconds to about 40 seconds (e.g., about 30 secs in someembodiments). If the duration of the fourth cleaning process C4 is tooshort, the magnetic layer ML1 may not be sufficiently cleaned. While ifthe duration of the fourth cleaning process C4 is too long, the hydrogenplasma of the fourth cleaning process C4 may cause unwanted consumptionto the magnetic layer ML1. On the other hand, the fourth cleaningprocess C4 can also activate the surface of the magnetic layer ML1. Thehydrogen plasma removes unwanted metal oxide on the magnetic layer ML1to make sure the surface of the magnetic layer ML1 is pure metal (e.g.,Co), such that the metal can act as a catalyst in the following graphenedeposition process.

It is noted that in the step of FIG. 6 , the valve V22 of the gasdelivery system 200 is turned off, such that only the gas (e.g., H₂) inthe source 204 is supplied into the processing chamber 100 duringcleaning of the substrate W1. That is, during the fourth cleaningprocess C4, the processing chamber 100 is free of aromatic hydrocarbon.On the other hand, during the fourth cleaning process C4, the pumpingsystem 500 is turned on, so as to pump out the gas (e.g., H₂) in theprocessing chamber 100. In greater detail, the gas (e.g., H₂) in theprocessing chamber 100 is pumped out to the pumping system 500 throughthe gas delivery line G2. In some embodiments, during the fourthcleaning process C4 of FIG. 8 , the gas environment of the processingchamber 100 is substantially a pure hydrogen (H₂) environment.

Referring back to FIG. 1 , the method M then proceeds to block S106where an aromatic hydrocarbon precursor is supplied into the processingchamber of the deposition system. After cleaning the magnetic layer ML1of FIG. 6 , the valve 24 of the gas delivery system 200 is turned off,such that supply of the gas (e.g., H₂) in the source 204 to theprocessing chamber 100 is stopped. Meanwhile, the RF system 300 isturned off. That is, the RF power of the RF system 300 in this step is azero value or negligibly small. On the other hand, the pumping system500 may pump out (remove) the remaining gas (e.g., hydrogen gas H₂) inthe processing chamber 100, so as to create a vacuum environment in theprocessing chamber 100.

With reference to FIG. 7 , in some embodiments of block S106, anaromatic hydrocarbon precursor can be provided into the processingchamber 100 and over the magnetic layer ML1. Subsequently, the valves 12and 22 of the gas delivery system 200 are turned on. As mentioned above,the source 202 is a liquid source. The liquid source may be liquidaromatic hydrocarbon, such as benzene (C₆H₆) or toluene (C₇H₈). In someembodiments, the aromatic hydrocarbon (e.g., benzene or toluene) is usedas a precursor for depositing a graphene layer discussed in FIG. 8 .Although the source 202 is a liquid aromatic hydrocarbon source, theliquid aromatic hydrocarbon may volatilize easily. Accordingly, as thevalve 12 is turned on, the liquid aromatic hydrocarbon in the source 202may volatilize and transform from a liquid phase to a gas phase, and thearomatic hydrocarbon gas (e.g., Benzene gas or Toluene gas) may flowthrough the mass flow controller 212 and then flows into the gasdelivery lines G12 and G1. For example, the aromatic hydrocarbon gasflows from the source 202 into the processing chamber 100 through thegas delivery lines G12 and G1. In some embodiments, the mass flowcontroller 212 is controlled such that the flow rate of the aromatichydrocarbon gas is in a range from about 0.5 sccm to about 1 sccm. Ifthe flow rate is too low (e.g., much lower than about 0.5 sccm), theconcentration of the aromatic hydrocarbon gas may be too low to providesufficient carbon. If the flow rate is too high (e.g., much higher thanabout 1 sccm), the carbon concentration may be too high and may affectthe quality of the graphene layer. In some embodiments, the aromatichydrocarbon gas is supplied into the processing chamber 100 withoutusing a carrier gas, such as Ar or H₂. That is, the gas environment ofthe processing chamber 100 is substantially a pure aromatic hydrocarbongas environment in this step, which will facilitate the formation of thegraphene layer in FIG. 8 .

In some embodiments, when a precursor for depositing a graphene layer ismethane (CH₄), acetylene (C₂H₂), or ethylene (C₂H₄), it will take alonger time to form a graphene layer because each molecule provides lesscarbon atoms. However, because the precursor for depositing the graphenelayer is an aromatic hydrocarbon precursor, a molecule of an aromatichydrocarbon can provide more carbon atoms (e.g., C₆H₆ or C₇H₈) than amolecule of methane (CH₄), acetylene (C₂H₂), or ethylene (C₂H₄).Accordingly, a deposition rate of the graphene layer can be increasedwhen using an aromatic hydrocarbon precursor in some embodiments of thepresent disclosure, which in turn allows for improving a productionefficiency of the graphene layer.

It is noted that in the step of FIG. 8 , the valve V24 of the gasdelivery system 200 has been turned off, such that only the aromatichydrocarbon in the source 202 is supplied into the processing chamber100. In some embodiments, the aromatic hydrocarbon gas is used as aprecursor in the deposition process in FIG. 8 , and thus aromatichydrocarbon gas can be interchangeably referred to as an aromatichydrocarbon precursor in the following content.

With reference again to FIG. 1 , the method M then proceeds to blockS107 where an RF power of an RF system equipped to the processingchamber is turned on, so as to deposit a graphene layer over themagnetic layer. With reference to FIG. 8 , in some embodiments of blockS107, the RF source 302 of the RF system 300 is turned on, so as togenerate plasma of aromatic hydrocarbon in the processing chamber 100.The aromatic hydrocarbon precursor is decomposed (or ionized) intoseveral active radical species, which constitute the plasma over themagnetic layer ML1. For example, the active radical species of theplasma may include aromatic radicals. “Aromatic radical” used hereinrefers to a radical including at least one ring of resonance bonds, suchas a benzene ring.

Next, the active radicals may be deposited on the surface of themagnetic layer ML1 and may diffuse on the surface of the magnetic layerML1. In some embodiments, some radicals will be gathered together andare close to each other. This mechanism is called “surface diffusion” ofthe radicals. A dehydrogenation reaction and a cyclization reaction maytake place, and then covalent bonding of the active radicals and/orrings form a graphene layer GL over the magnetic layer ML1.“Dehydrogenation” used herein refers to a chemical reaction thatinvolves the removal of hydrogen from an organic molecule. “Cyclization”used herein refers to the process in which the radicals are combined andtransformed into ‘benzene’ rings. Generally, the RF source 302 of the RFsystem 300 is turned on to decompose the aromatic hydrocarbon precursorinto active radicals, and the active radicals are then cyclized into agraphene layer.

Referring back to FIG. 8 , as mentioned above, before the RF source 302of the RF system 300 is turned on, the processing chamber 100 is alreadyfilled with the aromatic hydrocarbon precursor (see FIG. 7 ).Accordingly, once the RF source 302 of the RF system 300 is turned on,the plasma of aromatic hydrocarbon can be generated immediately, and thedeposition of the graphene layer GL takes place. That is, the RF system300 is operative to trigger the graphene deposition discussed herein.For example, the aromatic hydrocarbon precursor is decomposed intoseveral active radicals. Subsequently, a dehydrogenation reaction and acyclization reaction take place, thereby forming the graphene layer GLon the magnetic layer ML1.

In some embodiments, a flow rate of the aromatic hydrocarbon precursoris in a range from about 0.5 sccm to about 1 sccm. In some embodiments,the processing pressure is in a range from about 1×10⁻² torr to about2×10⁻² torr. In some embodiments, the RF power of the RF source 302 ofthe RF system 300 is in a range from about 250 W to about 400 W. If theRF power is too low (e.g., much lower than about 250 W), the aromatichydrocarbon may not be sufficiently decomposed. If the RF power is toohigh (e.g., much higher than about 400 W), the plasma may be too strongto cause unwanted etching to the magnetic layer ML1.

As shown in FIG. 8 , a high frequency induction heating process is alsoperformed on the magnetic layer ML1, which allows for speeding up thedeposition rate of the graphene layer GL. In greater detail, themagnetic layer ML1 may be heated by the RF system 300 through the coil110 wound around thereof to speed up the deposition rate of the graphenelayer GL on the magnetic layer ML1. The RF source 302 may supplyhigh-frequency alternating current to the coil 110. The alternatingcurrent may be supplied to the coil 110 at a radio frequency, such as afrequency greater than 1000 Hz. By way of example but not limiting thepresent disclosure, the alternating current may be in a frequencygreater than 300 kHz. The time variation in the high-frequencyalternating current produces a time-varying magnetic field MF as shownin FIG. 10B at the coil 110. Therefore, the magnetic layer ML1 ispositioned within the time-varying magnetic field MF generated by thecoil 110.

Next, the magnetic layer ML1 may be heated to a predeterminedtemperature within a few seconds or less by induced eddy currentgenerated by putting a coil 110 with high-frequency electrical currentin the vicinity of the magnetic layer ML1. In other words, bycontrolling the RF source 302, the desired heating temperature can beachieved within a few seconds or less. By using the method anddeposition systems described above, the graphene layer GL may begin toform when the temperature is greater than about 200° C. to about 400°C., and thus the graphene layer GL can be grown on the magnetic layerML1 without using a heater other than the RF system 300, by way ofexample but not limiting the present disclosure. Stated another way, thedeposition system 10 a is free of a heater other than the RF system 300.Thus, heating the magnetic layer ML1 by using this method may be activeand controllable, so as to speed up the deposition rate of the graphenelayer GL on the magnetic layer ML1.

By way of example but not limiting the present disclosure, the magneticlayer ML1 may be heated to about 800° C. for less than about 30 secs inthe operation of the RF source 302, which in turn allows for speeding upthe deposition rate of the graphene layer GL formed thereon, so as tolower the duration of deposition time of the graphene layer GL. That is,the duration of the deposition time of the graphene layer GL may bedetermined by the operation duration of the RF source 302 through thecoil 110, because the operation of the RF source 302 may actuate adehydrogenation reaction and a cyclization reaction, and then covalentbond the active radicals and/or rings of the aromatic hydrocarbon toform a graphene layer GL. In some embodiments, the deposition time ofthe graphene layer GL is defined as the duration between turning on theRF source 302 of the RF system 300 and turning off the RF source 302 ofthe RF system 300. In some embodiments, the duration of deposition timeof the graphene layer GL on the magnetic layer ML1 may be less thanabout 30 secs during the operation of the RF source 302. In someembodiments, the duration of deposition time of the graphene layer GL onthe magnetic layer ML1 may be less than or equal to about 12 secs (e.g.,about 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 secs) during the operation ofthe RF source 302. For example, in the operation of the RF source 302 todeposit the graphene layer GL, the magnetic layer ML1 may be heated toabout 200° C. for about 7 secs, may be heated to about 250° C. for about12 secs, may be heated to about 350° C. for about 18 secs, or may beheated to about 650° C. for about 32 secs. In some embodiments, aduration of deposition time of the graphene layer GL on the magneticlayer ML1 is shorter than a time duration of performing the fourthcleaning process C4. Therefore, a short deposition time of the graphenelayer GL may be achieved to improve a production efficiency of thegraphene layer.

In some embodiments, the magnetic layer ML1 has a better surface effectthan a non-magnetic material, and therefore has a faster heating rate,which in turn allows for speeding up the deposition rate of the graphenelayer GL formed thereon to ultimately result in lowering the duration ofdeposition time of the graphene layer GL.

In some embodiments, the magnetic layer ML1 having a greaterpermeability coefficient has a better surface effect than a magneticlayer having a lower permeability coefficient, and therefore has afaster heating rate. This in turn allows for speeding up the depositionrate of the graphene layer GL formed thereon to ultimately result inlowering the duration of deposition time of the graphene layer GL. Insome embodiments, the magnetic layer ML1 having a greater hysteresiscoefficient has a better surface effect than a magnetic layer having alower hysteresis coefficient, and therefore has a faster heating rate.This in turn allows for speeding up the deposition rate of the graphenelayer GL formed thereon to ultimately result in lowering the duration ofdeposition time of the graphene layer GL and improving a productionefficiency of the graphene layer.

Furthermore, an ambient temperature inside the processing chamber 100 ofthe deposition system 10 a may be determined by the RF source 302. Ingreater detail, the RF source 302 of the RF system 300 may generateplasma of aromatic hydrocarbon through the coil 110, which may raise theambient temperature in the processing chamber 100. By way of example butnot limiting the present disclosure, the ambient temperature inside theprocessing chamber 100 may be raised to about 200° C. to about 300° C.during the operation of the RF source 302. At the same time, themagnetic layer ML1 on the substrate W1 may be heated to about 800° C.for speeding up the deposition rate of the graphene layer GL formedthereon. That is, during the operation of the RF source 302, the ambienttemperature inside the processing chamber 100 is lower than thetemperature of the magnetic layer ML1. In some embodiments where asemiconductor device, such as a transistor, is formed on the substrateW1, the processing chamber 100 having an ambient temperature from about200° C. to about 300° C. would not destroy the semiconductor device,thereby improving the device yield. If the ambient temperature of theprocessing chamber 100 is higher than about 400° C., some devices formedon the substrate W1 may be destroyed.

FIG. 11A illustrates experimental results showing different operationtime durations of an RF source effect on temperatures of a magneticlayer. FIG. 11B illustrates a partial enlarged view of FIG. 11A. InFIGS. 11A and 11B, samples including a magnetic layer, such as a Cofoil, on a substrate were prepared and the temperatures of the magneticlayer were measured at the predetermined time durations of operation ofthe RF source. For example, the magnetic layer may be heated by an RFsystem through a coil wound around the samples. The RF source may supplyhigh-frequency alternating current to the coil. The alternating currentmay be supplied to the coil at a radio frequency, such as a frequencygreater than 1000 Hz. By way of example but not limiting the presentdisclosure, the alternating current may be in a frequency greater than300 kHz. In the example shown in FIGS. 11A and 11B, the RF source wasoperated at predetermined time durations of about 0, 7, 12, 20, 30, 250,and 600 secs.

As shown in FIGS. 11A and 11B, before the RF source of a RF system isturned on (i.e., the predetermined time is about 0 sec), the temperatureof the magnetic layer is about room temperature, such as about 25° C. insome embodiments. Once the RF source of the RF system is turned on, ahigh frequency induction heating process is performed on the magneticlayer, which allows for heating the magnetic layer within a few seconds.In the example shown in FIGS. 11A and 11B, the magnetic layer may beheated to about 200° C. in about 7 seconds, heated to about 250° C. inabout 12 seconds, and heated to about 800° C. in about 30 secs, which inturn allows for speeding up the deposition rate of a graphene layerformed thereon, so as to lower the duration of deposition time of thegraphene layer. Therefore, by controlling the RF source, the desiredheating temperature can be achieved within a few seconds. By using themethod and deposition systems described above, the graphene layer maybegin to form when the temperature is greater than about 200° C. toabout 400° C., and thus the graphene layer can be grown on the magneticlayer without using a heater other than the RF system, by way of examplebut not limiting the present disclosure.

Raman spectroscopy is a characterization technique for a graphene layerGL. Carbon-based materials, such as graphene, may have three intenseRaman features including a defect band (D band), a band related toin-plan vibration of sp2 carbon (G band), and a stacking order (2Dband). For monolayer graphene, the g band has a Raman Shift located atabout 1580 cm′, the d band has a Raman Shift located at about 1350 cm⁻¹,and the 2d band has a Raman Shift located at about 2700 cm⁻¹. Therelative intensity (a.u.) of the g band frequency of Raman spectra maybe used as a measure for a number of features that provide informationregarding sample purity, geometry, and the metallic or semi-conductingnature of the material. Another prominent feature in the Raman spectraof carbon-based materials is the d band. The d band is sensitive todifferences in the carbon network that is characteristic of manycarbon-based materials, and the intensity of the d band may provideinformation on the electronic character of a particular material.Because a carbon lattice may contain aromatic carbons that are sp2hybridized and may be substantially more conductive, it may bebeneficial to select for the graphene layer GL having fewer numbers ofnon-aromatic sp3 hybridized carbon sites, or “defects” in the carbonlattice. For example, higher intensity in the d band in a Raman spectrummay indicate that a particular sample has a higher concentration ofdefects and may not be as conductive as a sample having a relativelylower d band intensity.

In some embodiments, a ratio of the d band to the g band (d/g ratio) mayalso be used as a measure of both the purity of a sample and, inrelatively pure samples, can be used to characterize the defects presenton the graphene layer GL, where a lower d/g ratio may indicate the asample containing higher general concentrations of sp2 carbons, a morecomplete carbon lattice on the graphene layer GL, and higher generalelectrical and/or thermal conductivity.

In some embodiments, by using the method and deposition systemsdescribed above, the d/g ratio of the graphene layer GL formed on themagnetic layer ML1 as measured by Raman spectroscopy may be less thanabout 1 when the deposition time thereof is longer than about 3 secs. Insome embodiments, by using the method and deposition systems describedabove, the d/g ratio of the graphene layer GL formed on the magneticlayer ML1 as measured by Raman spectroscopy may be less than about 0.3when the deposition time thereof is longer than about 10 secs. In someembodiments, by using the method and deposition systems described above,the d/g ratio of the graphene layer GL formed on the magnetic layer ML1as measured by Raman spectroscopy may be less than about 0.1 when thedeposition time thereof is longer than about 12 secs. Therefore, byusing the method and deposition systems described above, a shortdeposition time (e.g., about 3-30 secs in some embodiments, such asabout 3, 5, 20, or 30 seconds) of the graphene layer GL may be achievedto reduce the d/g ratio, which in turn allows for lowering the defectdensity (e.g., d/g ratio < about 0.5 in some embodiments, such as about0.1, 0.2, 0.3, 0.4, or 0.5) and improving the quality and uniformity ofthe dgraphene layer GL.

FIGS. 12A to 12C illustrate experimental results of a Raman spectrum ofgraphene formed over a magnetic layer with different operation timedurations of the RF source. In FIGS. 12A to 12C, the samples including agraphene layer formed by a precursor (e.g., benzene (C₆H₆)) on amagnetic layer (e.g., Co foil) were prepared and intensities of Ramanshift of the graphene layer were measured after the predetermined timedurations of operation of the RF source. The RF source may be suppliedto the samples at a radio frequency, such as a frequency greater than1000 Hz. By way of example but not limiting the present disclosure, thealternating current may be in a frequency greater than 300 kHz. For thesamples shown in FIGS. 12A to 12C, the g band has a Raman Shift locatedat about 1580 cm⁻¹, the d band has a Raman Shift located at about 1350cm⁻¹, and the 2d band has a Raman Shift located at about 2700 cm⁻¹. Inthe example shown in FIG. 12A, the RF source is operated atpredetermined time durations about 3, 5, 10, 20, and 30 secs. In theexample shown in FIG. 12B, the RF source is operated at thepredetermined time duration about 7 secs. In the example shown in FIG.12C, the RF source is operated at the predetermined time duration about12 secs. FIG. 13 illustrates experimental results showing differentoperation time durations of the RF source effect on ratios of the d bandto the g band (d/g ratio) of graphene formed over the magnetic layer ofFIGS. 12A to 12C.

As shown in FIGS. 12A, 12B, 12C, and 13 , the d/g ratio of the graphenelayer formed on the magnetic layer as measured by Raman spectroscopy isabout 1 when the time duration is about 3 secs, the d/g ratio of thegraphene layer formed on the magnetic layer as measured by Ramanspectroscopy is about 0.3 when the time duration is about secs, and thed/g ratio of the graphene layer formed on the magnetic layer as measuredby Raman spectroscopy is less than about 0.1 when the time duration isabout secs. Therefore, as shown in the experimental results of FIG. 13 ,by using the method and deposition systems described above, a shortdeposition time of the graphene layer may be achieved to reduce the d/gratio, which in turn allows for lowering the defect density andimproving the quality of the graphene layer.

In some embodiments, the graphene layer GL can be deposited over a largearea which depends on the sizes of the RF coil 110 and the processingchamber 100. For example, in some embodiments where the area of themagnetic layer ML1 may be in a range from about 1*2 cm² to about 12*2cm², experimental results show that the graphene layer GL has a uniformregion having an area about 8*2 cm′ to about 10*2 cm² (e.g., about 9*2cm²).

After an entirety of the magnetic layer ML1 is covered by the graphenelayer GL and/or after the graphene layer GL is grown to a desiredthickness, the RF source 302 of the RF system 300 can be turned off, soas to stop depositing the graphene layer GL. In some embodiments, thedeposition time of the graphene layer GL formed on the magnetic layerML1 may be less than about 30 seconds, and the graphene layer GL mayhave a thickness in a range from about 0.7 nm to about 7 nm, layers in arange from about 2 to about 20, and a sheet resistance lower than about100 Ω/sq, by way of example but not limiting the present disclosure.FIGS. 34 and 35 illustrate schematic transmission electron microscopyimages showing different graphene growth experimental results formed indifferent deposition time durations. In FIG. 34 , when the depositiontime of the graphene layer GL2 formed on the magnetic layer ML2 is about12 seconds, the graphene layer GL2 may have a thickness of about 5.74 nmin about 17 layers. In FIG. 35 , when the deposition time of thegraphene layer GL3 formed on the magnetic layer ML3 is about 7 seconds,the graphene layer GL3 may have a thickness of about 1.8 nm in about 4layers. In the example shown in FIG. 35 , the magnetic layer may beheated to about 200° C. in about 7 seconds. In the example shown in FIG.34 , the magnetic layer may be heated to about 250° C. in about 12seconds. Thus, by using the method and deposition systems describedabove, a short deposition time of the graphene layer GL formed on themagnetic layer ML1 may be achieved to improve a production efficiency,quality, and sheet resistance of the graphene layer. Moreover, asillustrated in FIGS. 34 and 35 , the graphene layer GL3 formed in ashorter time duration may have a higher thickness non-uniformity thanthe graphene layer GL2 formed in a longer time duration, which meansthat the thickness uniformity of graphene may increases as depositiontime increases.

FIG. 14 illustrates experimental results showing different operationtime durations of the RF (radio frequency) source effect on electricalproperties. In FIG. 14 , the samples including a graphene layer formedby a precursor (e.g., benzene (C₆H₆)) and a magnetic layer (e.g., Cofoil) were prepared, and sheet resistance (Ω/sq) was measured after thepredetermined time durations of operation of the RF source. The RFsource may be supplied to the samples at a radio frequency, such as afrequency greater than 1000 Hz. By way of example but not limiting thepresent disclosure, the alternating current may be in a frequencygreater than 300 kHz. In the example shown in FIG. 14 , the RF source isoperated at predetermined time durations about 3, 5, 10, 12, 30, 60, and120 secs. As shown in FIG. 14 , the sheet resistance (Ω/sq) of thegraphene layer formed on the magnetic layer may be less than about 500(e.g., about 480) when the time duration is about 3 secs, the sheetresistance (Ω/sq) of the graphene layer formed on the magnetic layer maybe less than about 200 (e.g., about 190) when the time duration is about5 secs, and the sheet resistance (Ω/sq) of the graphene layer formed onthe magnetic layer is about 100 when the time duration is about 12 secs.Therefore, as shown in the experimental results of FIG. 14 , by usingthe method and deposition systems described above, a short depositiontime of the graphene layer may be achieved to improve a sheet resistanceof the graphene layer within a few seconds.

It is noted that in the present disclosure, the aromatic hydrocarbonprecursor is supplied into the processing chamber 100 without using acarrier gas, such as Ar or H₂. This will improve the quality of thedeposited graphene layer GL, because the RF power provided by the RFsystem 300 may transform the carrier gas into plasma (e.g., Ar plasma orH₂ plasma), while the such plasma may etch the graphene layer GL duringdeposition.

Referring back to FIG. 1 , the method M then proceeds to block S108where the substrate is moved out from the processing chamber of thedeposition system. With reference to FIG. 9 , in some embodiments ofblock S108, after the RF source 302 of the RF system 300 (see FIG. 8 )is turned off, the substrate W1 is moved out from the processing chamber100 (see FIG. 9 ). In some embodiments, before moving out the substrateW1 from the processing chamber 100, the valve 22 of the gas deliverysystem 200 may be turned off, so as to stop providing aromatichydrocarbon precursor into the processing chamber 100.

Reference is made to FIGS. 15 to 32 . FIGS. 15 to 32 illustrate a methodin various stages of forming a semiconductor device in accordance withsome embodiments of the present disclosure.

Reference is made to FIG. 15 . An initial structure is received. Theinitial structure includes a substrate 610. The substrate 610 includesan N-well region 600N and a P-well region 600P, in which the N-wellregion 600N may be doped with N-type impurities, and the P-well region600P may be doped with P-type impurities. The substrate 610 may be asemiconductor material and may include known structures including agraded layer or a buried oxide, for example. Other materials, such asgermanium, quartz, sapphire, and glass could alternatively be used forthe substrate 610. Alternatively, the silicon substrate 610 may be anactive layer of a semiconductor-on-insulator (SOI) substrate or amulti-layered structure such as a silicon-germanium layer formed on abulk silicon layer.

Isolation structures 605 are disposed in the substrate 610. In someembodiments, the isolation structures 605 may include oxide, such assilicon dioxide. The isolation structures 605, which act as a shallowtrench isolation (STI) around the P-well region 600P from the N-wellregion 600N, may be formed by chemical vapor deposition (CVD) techniquesusing tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor.

A gate structure 600A is disposed over the P-well region 600P of thesubstrate 610, and a gate structure 600B is disposed over the N-wellregion 600N of the substrate 610. In some embodiments, each of the gatestructure 600A and the gate structure 600B includes a gate dielectric602 and a gate electrode 604. In some embodiments, the gate dielectric602 may be, for example, silicon oxide, silicon nitride, a combinationthereof, or the like, and may be deposited or thermally grown accordingto acceptable techniques. In some embodiments, the gate electrode 604may include polycrystalline-silicon (poly-Si) or poly-crystallinesilicon-germanium (poly-SiGe). In some other embodiments, the gatestructure 600A and the gate structure 600B may be metal gate structures,which include a high-k dielectric layer, a work function metal layerover the high-k dielectric layer, and a gate metal over the workfunction metal layer.

Capping layers 625 are disposed over the gate structures 600A and 600B.In some embodiments, the capping layers 625 may be oxide. A plurality ofgate spacers 612 are disposed on opposite sides of the gate structure600A and the gate structure 600B. In some embodiments, the gate spacers612 may include SiO₂, Si₃N₄, SiO_(x)N_(y), SiC, SiCN films, SiOC, SiOCNfilms, and/or combinations thereof.

Source/drain structures 620N are disposed in the P-well region 620P ofthe substrate 610 and on opposite sides of the gate structure 600A, andsource/drain structures 620P are disposed in the N-well region 620N ofthe substrate 610 and on opposite sides of the gate structure 600B. Insome embodiments, the source/drain structures 620N may be doped withN-type impurities, and the source/drain structures 620P may be dopedwith p-type impurities. In some embodiments, the source/drain structures620N, 620P may be may be formed by performing an epitaxial growthprocess that provides an epitaxy material over the substrate 610, andthus the source/drain structures 620N, 620P can be interchangeablyreferred to as epitaxy structures 620N, 620P in this context. In variousembodiments, the source/drain structures 620N, 620P may include Ge, Si,GaAs, AlGaAs, SiGe, GaAsP, SiP, or other suitable materials.

A contact etch stop layer (CESL) 630 is disposed over the isolationstructures 605 and over the capping layers 625. An interlayer dielectric(ILD) layer 640 is disposed over the CESL 630 and surrounds the gatestructures 600A and 600B. In some embodiments, the CESL 630 includessilicon nitride, silicon oxynitride or other suitable materials. TheCESL 630 can be formed using, for example, plasma enhanced CVD, lowpressure CVD, ALD or other suitable techniques. In some embodiments, theILD layer 640 may include silicon oxide, silicon nitride, siliconoxynitride, tetraethoxysilane (TEOS), phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), low-k dielectric material, and/orother suitable dielectric materials. Examples of low-k dielectricmaterials include, but are not limited to, fluorinated silica glass(FSG), carbon doped silicon oxide, amorphous fluorinated carbon,parylene, bis-benzocyclobutenes (BCB), or polyimide. The ILD layer 640may be formed using, for example, CVD, ALD, spin-on-glass (SOG) or othersuitable techniques.

Source/drain contacts 650 are disposed in the ILD layer 640 and contactthe source/drain structures 620A and 620P. In some embodiments, eachsource/drain contact 650 includes a liner 652 and a plug 654. The liner652 is between the plug 654 and the underlying source/drain structures600A or 600B. In some embodiments, the liner 652 assists with thedeposition of the plug 654 and helps to reduce diffusion of a materialof the plug 654 through the gate spacers 612. In some embodiments, theliner 652 includes titanium (Ti), titanium nitride (TiN), tantalum (Ta),tantalum nitride (TaN), or another suitable material. The plug 654includes a conductive material, such tungsten (W), copper (Cu), aluminum(Al), ruthenium (Ru), cobalt (Co), molybdenum (Mo), nickel (Ni), orother suitable conductive materials.

An etch stop layer (ESL) 700 is disposed over the ILD layer 640 and thesource/drain contacts 650. An inter-metal dielectric (IMD) layer 705 isdisposed over the ESL 700. The material and the formation method of theESL 700 are similar to those of the CESL 630. Moreover, the material andthe formation method of the IMD layer 705 are similar to those of theILD layer 640.

Reference is made to FIG. 16 . The ESL 700 and the IMD layer 705 arepatterned to form openings O1. Subsequently, a liner 710 and a magneticlayer 715 are formed in the openings O1. In some embodiments, the liner710 includes titanium (Ti), titanium nitride (TiN), tantalum (Ta),tantalum nitride (TaN), or another suitable material. In someembodiments, the magnetic layer 715 may be made of a higher permeabilitycoefficient material than the liner 710. The magnetic layer 715 may bemade of a higher hysteresis coefficient material than the liner 710. Themagnetic layer 715 may be made of a lower conductivity material than theliner 710. In some embodiments, the magnetic layer 715 may have agreater thickness than the liner 710.

In some embodiments, the magnetic layer 715 may be made of a magneticmaterial, such as iron (Fe), cobalt (Co), nickel (Ni), proper alloys,suitable materials, or combinations thereof. By way of example but notlimiting the present disclosure, the magnetic material may be made ofCoPt, CoPd, FePt, or FePd. In some embodiments, the magnetic material inthe magnetic layer 715 has an atomic percentage greater than or equal toabout 10% (e.g., about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%).In some embodiments, the magnetic material is evenly dispersed in themagnetic layer 715. That is, any position in the magnetic layer 715substantially has the same atomic percentage of the magnetic material.In some embodiments, the magnetic material in an upper portion of themagnetic material has a greater atomic percentage than a lower portionof the magnetic layer 715. In some embodiments, an entirety of themagnetic layer 715 is made of the same magnetic material.

In some embodiments, the magnetic layer 715 may include a plurality ofmagnetic materials. By way of example but not limiting the presentdisclosure, the plurality of magnetic materials may include iron (Fe),cobalt (Co), nickel (Ni), proper alloys, or other suitable materials,such as CoFeTa, NiFe, CoFe, NiCo. By way of example but not limiting thepresent disclosure, the magnetic layer 715 may include nickel with anatomic percentage in a range from about 70% to about 90% and iron withan atomic percentage in a range from about 10% to about 30%. By way ofexample but not limiting the present disclosure, the magnetic layer 715may include nickel with an atomic percentage in a range from about 30%to about 50%, zinc with an atomic percentage in a range from about 10%to about 30% and copper with an atomic percentage in a range from about10% to about 30% plus ferric oxide (e.g., Fe₂O₄) with an atomicpercentage in a range from about 0.5% to about 10%. By way of examplebut not limiting the present disclosure, the magnetic layer 715 mayinclude yttrium with an atomic percentage in a range from about 70% toabout 90% and bismuth with an atomic percentage in a range from about10% to about 30% plus ferric oxide (e.g., Fe₅O₁₂) with an atomicpercentage in a range from about 0.5% to about 10%. By way of examplebut not limiting the present disclosure, the magnetic layer 715 mayinclude cobalt with an atomic percentage in a range from about 85% toabout 95%, zirconium with an atomic percentage in a range from about2.5% to about 7.5% and tantalum with an atomic percentage in a rangefrom about 2.5% to about 7.5%.

In some embodiments, the magnetic layer 715 may be made of nitride orsilicide of a magnetic material, such as nitride or silicide of iron(Fe), cobalt (Co), nickel (Ni), proper alloys thereof, suitablematerials, or combinations thereof. In some embodiments, the magneticlayer 715 may be made of a ferromagnetic material. By way of example butnot limiting the present disclosure, the magnetic layer 715 may includean alloy of a rare earth metal and a transition metal (RE-TM alloy),such as terbium iron cobalt (TbFeCo), terbium cobalt (TbCo), RE-cobaltpalladium (RE-CoPd), RE-cobalt platinum (RE-CoPt), suitable materials,or combinations thereof. In some embodiments, the magnetic layer 715 maybe made of a magnetic material with a dopant, such as boron (B),therein. By way of example but not limiting the present disclosure, themagnetic layer 715 may be made of CoFeB.

Reference is made to FIG. 17 . A graphene layer 720 is deposited overthe magnetic layer 715. In some embodiments, the graphene layer 720 canbe formed by using the method and deposition systems described in FIGS.1-10B, and thus relevant details will not be repeated hereinafter. Forexample, the magnetic layer 715 is similar to the magnetic layer ML1 ofFIGS. 2-9 , and the graphene layer 720 is similar to the graphene layerGL of FIGS. 2-9 . In some embodiments, the thickness of the graphenelayer 720 is in a range from about 1 nm to about 3 nm. With respect tothe deposition process of FIG. 8 , the deposition time of the graphenelayer 720 may be in a range from about 3 seconds to about 15 seconds(e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or seconds). Insome embodiments, the graphene layer 720 may have a smaller thicknessthan the magnetic layer 715.

Reference is made to FIG. 18 . A filling metal 730 is deposited over thegraphene layer 720 and fills the openings O1. In some embodiments, thefilling metal 730 is made of a highly conductive material. In someembodiments, the filling metal 730 may include metal, such as tungsten(W), ruthenium (Ru), aluminum (Al), copper (Cu), or other suitableconductive materials. In some embodiments, the conductive material 170may be deposited by CVD, physical vapor deposition (PVD), sputterdeposition, ALD, electroplating, or other techniques suitable fordepositing conductive materials. In some embodiments, the magnetic layer715 may be made of a higher permeability coefficient material than thefilling metal 730. The magnetic layer 715 may be made of a higherhysteresis coefficient material than the filling metal 730. The magneticlayer 715 may be made of a lower conductivity material than the fillingmetal 730.

Reference is made to FIG. 19 . A chemical mechanical polishing (CMP)process is performed to remove excessive materials of the filling metal730, the graphene layer 720, the magnetic layer 715, and the liner 710until the IMD layer 705 is exposed. In some embodiments, the remainingfilling metal 730, the graphene layer 720, the magnetic layer 715, andthe liner 710 can be referred to as a metal-1 (M1) layer in a back endof line (BEOL) process.

Reference is made to FIG. 20 . A plurality of graphene layers 740 aredeposited on the remaining filling metal 730, the graphene layer 720,the magnetic layer 715, and the liner 710. In greater detail, thegraphene layer 720 grows on the filling metal 730 because the fillingmetal 730 is heated by the surrounding magnetic layer 715. The fillingmetal 730 may be heated to a predetermined temperature (e.g., greaterthan about 200° C. to about 400° C. in some embodiments) within a fewseconds (e.g., about 3-30 seconds in some embodiments) through thesurrounding magnetic layer 715 by the RF source of the deposition systemof the present disclosure. Thus, heating the filling metal 730 throughthe surrounding magnetic layer 715 by using a high frequency inductionheating process of the present disclosure may lower the duration ofdeposition time of the graphene layer, which in turn allows forimproving the production efficiency, quality, and sheet resistance ofthe graphene layer. In some embodiments, the graphene layers 740 tend togrow on a graphene surface and/or a metal surface rather than on adielectric surface. As an example in FIG. 20 , the graphene layers 740are selectively formed on the filling metal 730, the graphene layer 720,the magnetic layer 715, and the liner 710, while the graphene layers 740are not formed on the IMD layer 705. In some embodiments, the graphenelayers 740 can be formed by using the method and deposition systemsdescribed in FIGS. 1-10B, and thus relevant details will not be repeatedhereinafter. For example, the graphene layers 740 are similar to thegraphene layer GL of FIGS. 2-9 . In some embodiments, the thickness ofthe graphene layers 740 is in a range from about 1 nm to about 3 nm.With respect to the deposition process of FIG. 8 , the deposition timeof the graphene layers 740 may be in a range from about 3 seconds toabout 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,or 15 seconds).

Reference is made to FIG. 21 . An ESL 800, an IMD layer 802, an ESL 804,and an IMD layer 806 are formed sequentially over the IMD layer 705. TheESLs 800 and 804 are similar to the ESL 700, the IMD layers 802 and 806are similar to the IMD layer 705, and thus relevant details will not berepeated for brevity. This is described in greater detail with referenceto FIG. 21 , the ESL 800 has non-uniform thickness due to the underlyinggraphene layers 740. That is, the ESL 800 on the graphene layers 740 mayhave a thinner thickness than that on the IMD layer 705. In someembodiments, the ESL 800 has uniform thickness, but the IMD layer 802has non-uniform thickness due to the ESL 800 being conformal over thegraphene layers 740.

Reference is made to FIG. 22 . The ESL 800, the IMD layer 802, the ESL804, and the IMD layer 806 are patterned to form via openings O2. Insome embodiments, the via openings O2 are aligned with and expose thegraphene layers 740. In some embodiments, via openings O2 may be formedby, for example, forming a patterned photoresist layer over the IMDlayer 806, followed by an etching process to remove portions of the ESL800, the IMD layer 802, the ESL 804, and the IMD layer 806, and thenremoving the photoresist layer.

Reference is made to FIG. 23 . The ESL 804 and the IMD layer 806 arepatterned to form trenches TR2 that are aligned above the via openingsO2. In some embodiments, the trenches TR2 may be formed by, for example,forming a patterned photoresist layer over the IMD layer 806, followedby an etching process to remove portions of the ESL 804, and the IMDlayer 806, and then removing the photoresist layer.

Reference is made to FIG. 24 . A liner 810, a magnetic layer 815, and agraphene layer 820 are formed sequentially over the IMD layer 806 and inthe via openings O2 and the trenches TR2. The liner 810 and the magneticlayer 815 are similar to the liner 710 and the magnetic layer 715,respectively, and thus relevant details will not be repeated forbrevity. In some embodiments, the graphene layer 820 can be formed byusing the method and deposition systems described in FIGS. 1-10B, andthus relevant details will not be repeated hereinafter. For example, thegraphene layer 820 is similar to the graphene layer GL of FIGS. 2-9 . Insome embodiments, the thickness of the graphene layer 820 is in a rangefrom about 3 nm to about 5 nm. With respect to the deposition process ofFIG. 8 , the deposition time of the graphene layer 820 may be in a rangefrom about 3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, or 15 seconds). In some embodiments, the graphenelayer 820 may have a smaller thickness than the magnetic layer 815. Insome embodiments, the graphene layer 820 is thicker than the graphenelayer 720, and the deposition time of the graphene layer 820 is longerthan the deposition time of the graphene layer 720. In some embodiments,the magnetic layer 815 may be made of a higher permeability coefficientmaterial than the liner 810. The magnetic layer 815 may be made of ahigher hysteresis coefficient material than the liner 810. The magneticlayer 815 may be made of a lower conductivity material than the liner810. In some embodiments, the magnetic layer 815 may have a greaterthickness than the liner 810.

Reference is made to FIG. 25 . A filling metal 830 is deposited over thegraphene layer 820 and fills the via openings O2 and the trenches TR2.The filling metal 830 is similar to the filling metal 730, and thusrelevant details will not be repeated hereinafter. In some embodiments,the magnetic layer 815 may be made of a higher permeability coefficientmaterial than the filling metal 830. The magnetic layer 815 may be madeof a higher hysteresis coefficient material than the filling metal 830.The magnetic layer 815 may be made of a lower conductivity material thanthe filling metal 830.

Reference is made to FIG. 26 . A chemical mechanical polishing (CMP)process is performed to remove excessive materials of the filling metal830, the graphene layer 820, the magnetic layer 815, and the liner 810until the IMD layer 806 is exposed. In some embodiments, the remainingfilling metal 830, the graphene layer 820, the magnetic layer 815, andthe liner 810 can be referred to as a metal-2 (M2) layer in a back endof line (BEOL) process. In some embodiments, the line width of themetal-2 layer is greater than the line width of the metal-1 layer (seeFIG. 19 ), and so the graphene layers 820 of the metal-2 layer can beformed thicker than the graphene layer 720 of the metal-1 layer.

Reference is made to FIG. 27 . A plurality of graphene layers 840 aredeposited on the remaining filling metal 830, the graphene layer 820,the magnetic layer 815, and the liner 810. In some embodiments, thegraphene layers 840 tend to grow on a graphene surface and/or a metalsurface rather than on a dielectric surface. For example, the graphenelayers 840 are selectively formed on the filling metal 830, the graphenelayer 820, the magnetic layer 815, and the liner 810, while the graphenelayers 840 are not formed on the IMD layer 806. In some embodiments, thegraphene layers 840 can be formed by using the method and depositionsystems described in FIGS. 1-10B, and thus relevant details will not berepeated hereinafter. For example, the graphene layers 840 are similarto the graphene layer GL of FIGS. 2-9 . In some embodiments, thethickness of the graphene layer 840 is in a range from about 3 nm toabout 5 nm. With respect to the deposition process of FIG. 8 , thedeposition time of the graphene layers 840 may be in a range from about3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, or 15 seconds).

Reference is made to FIG. 28 . An ESL 900, an IMD layer 902, an ESL 904,and an IMD layer 906 are formed sequentially over the IMD layer 806. TheESLs 900 and 904 are similar to the ESL 700, the IMD layers 902 and 906are similar to the IMD layer 705, and thus relevant details will not berepeated for brevity.

Reference is made to FIG. 29 . The ESL 900, the IMD layer 902, the ESL904, and the IMD layer 906 are patterned to form via openings O3 andtrenches TR3 above the via openings O3. The formation of the viaopenings O3 and the trenches TR3 are similar respectively to the viaopenings O2 and the trenches TR2 described in FIGS. 23 and 24 , and thusrelevant details will not be repeated for brevity.

Next, a liner 910, a magnetic layer 915, and a graphene layer 920 areformed sequentially over the IMD layer 906 and in the via openings O3and the trenches TR3. The liner 910 and the magnetic layer 915 aresimilar to the liner 710 and the magnetic layer 715, respectively, andthus relevant details will not be repeated for brevity. In someembodiments, the graphene layer 920 can be formed by using the methodand deposition systems described in FIGS. 1-10B, and thus relevantdetails will not be repeated hereinafter. In some embodiments, thethickness of the graphene layer 920 is in a range from about 3 nm toabout 10 nm. With respect to the deposition process of FIG. 8 , thedeposition time of the graphene layer 920 may be in a range from about 3seconds to about 20 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, or 20 seconds). In some embodiments, thegraphene layer 920 may have a smaller thickness than the magnetic layer915. In some embodiments, the graphene layer 920 is thicker than thegraphene layer 820, and the deposition time of the graphene layer 920 islonger than the deposition time of the graphene layer 820. In someembodiments, the magnetic layer 915 may be made of a higher permeabilitycoefficient material than the liner 910. The magnetic layer 915 may bemade of a higher hysteresis coefficient material than the liner 910. Themagnetic layer 915 may be made of a lower conductivity material than theliner 910. In some embodiments, the magnetic layer 915 may have agreater thickness than the liner 910.

Reference is made to FIG. 30 . A filling metal 930 is deposited over thegraphene layer 920 and fills the via openings O3 and trenches TR3. Thefilling metal 930 is similar to the filling metal 730, and thus relevantdetails will not be repeated hereinafter. In some embodiments, themagnetic layer 915 may be made of a higher permeability coefficientmaterial than the filling metal 930. The magnetic layer 915 may be madeof a higher hysteresis coefficient material than the filling metal 930.The magnetic layer 915 may be made of a lower conductivity material thanthe filling metal 930.

Reference is made to FIG. 31 . A chemical mechanical polishing (CMP)process is performed to remove excessive materials of the filling metal930, the graphene layer 920, the magnetic layer 915, and the liner 910until the IMD layer 906 is exposed. In some embodiments, the remainingfilling metal 930, the graphene layer 920, the magnetic layer 915, andthe liner 910 can be referred to as a metal-3 (M3) layer in a back endof line (BEOL) process. In some embodiments, the line width of themetal-3 layer is greater than the line width of the metal-2 layer (seeFIG. 26 ), and so the graphene layers 920 of the metal-3 layer can beformed thicker than the graphene layer 820 of the metal-2 layer.

Reference is made to FIG. 32 . A plurality of graphene layers 940 aredeposited on the remaining filling metal 930, the graphene layer 920,the magnetic layer 915, and the liner 910. In some embodiments, thegraphene layers 940 tend to grow on a graphene surface and/or a metalsurface rather than on a dielectric surface. For example, the graphenelayers 940 are selectively formed on the filling metal 930, the graphenelayer 920, the magnetic layer 915, and the liner 910, while the graphenelayers 940 are not formed on the IMD layer 906. In some embodiments, thegraphene layers 940 can be formed by using the method and depositionsystems described in FIGS. 1 −10B, and thus relevant details will not berepeated hereinafter. In some embodiments, the thickness of the graphenelayers 940 is in a range from about 3 nm to about 10 nm. With respect tothe deposition process of FIG. 8 , the deposition time of the graphenelayers 940 may be in a range from about 3 seconds to about 20 seconds(e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, or 20 seconds). In some embodiments, the graphene layers 940 arethicker than the graphene layers 840, and the deposition time of thegraphene layers 940 is longer than the deposition time of the graphenelayers 840.

Next, a plurality of conductive layers 950 are formed respectively overthe graphene layers 940. In some embodiments, conductive layers 950 maybe aluminum, or other suitable conductive materials. In someembodiments, the conductive layers 950 can be formed by PVD, CVD, ALD,or other suitable process. In some embodiments, the conductive layers950 can be formed by, for example, depositing a conductive material overthe substrate 610, followed by a photolithography process to pattern theconductive material to form the conductive layers 950.

FIG. 33 illustrates another semiconductor device at a stagecorresponding to FIG. 28 according to some alternative embodiments ofthe present disclosure. A difference between FIGS. 32 and 33 is that theliner 710, the liner 810, and the liner 910 are omitted. Therefore, themagnetic layer 715 is formed to directly contact the IMD layer 705. Themagnetic layer 815 is formed to directly contact the IMD layer 802, theESL 804, and the IMD layer 806 and lands on the graphene layer 740. Themagnetic layer 915 is formed to directly contact the IMD layer 902, theESL 904, and the IMD layer 906 and lands on the graphene layer 840, suchthat the conductivity of interconnects of the semiconductor device maybe improved. In some embodiments, the magnetic layer 715, 815, and/or915 is configured to block diffusion of the material of the fillingmetal 730, 830, and/or 930 to the IMD layer 705, 802, 806, 902, and/or906.

Based on the above discussion, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. The graphene layer of the presentdisclosure is deposited on a magnetic layer by using a deposition systemwith an RF source. An advantage is that a short deposition time (e.g.,about 3-30 seconds in some embodiments) of the graphene layer GL formedon the magnetic layer may be achieved to improve the productionefficiency, quality, and sheet resistance of the graphene layer. Ingreater detail, the graphene layer may begin to be formed when thetemperature is high enough (e.g., greater than about 200° C. to about400° C. in some embodiments). The magnetic layer whereon the graphenelayer will be formed may be heated to a predetermined temperature (e.g.,greater than about 200° C. to about 400° C. in some embodiments) withina few seconds (e.g., about 3-30 seconds in some embodiments) by the RFsource of the deposition system of the present disclosure. Thus, heatingthe magnetic layer by using a high frequency induction heating processof the present disclosure may lower the duration of deposition time ofthe graphene layer, which in turn allows for improving the productionefficiency, quality, and sheet resistance of the graphene layer.

In some embodiments, a plasma enhanced chemical vapor deposition (PECVD)method includes loading a wafer having a magnetic layer thereon into aprocessing chamber equipped with a radio frequency (RF) system,introducing an aromatic hydrocarbon precursor into the processingchamber, and turning on an RF source of the RF system to decompose thearomatic hydrocarbon precursor into active radicals at a frequencygreater than about 1000 Hz to form a graphene layer over the magneticlayer. In some embodiments, the frequency of the RF source is greaterthan about 300 kHz. In some embodiments, the magnetic layer is made ofcobalt. In some embodiments, the magnetic layer is made of nickel. Insome embodiments, the magnetic layer is made of iron. In someembodiments, the magnetic layer has a permeability coefficient greaterthan about 5×10⁻⁵ (H/m). In some embodiments, the magnetic layer has ahysteresis coefficient greater than about 300 (A/m). In someembodiments, turning on the RF source of the RF system is performed at atime duration of less than about 60 seconds. In some embodiments, themethod further includes performing an H₂ plasma treatment on the waferto clean the magnetic layer after loading the wafer and prior tointroducing the aromatic hydrocarbon precursor, wherein the turning onthe RF source of the RF system is performed at a time duration shorterthan a time duration of performing the H₂ plasma treatment. In someembodiments, turning on the RF source of the RF system is performed suchthat an ambient temperature inside the processing chamber is less thanabout 300° C. In some embodiments, turning on the RF source of the RFsystem is performed to heat the magnetic layer to a temperature greaterthan about 300° C. In some embodiments, turning on the RF source of theRF system is performed such that an ambient temperature inside theprocessing chamber is less than a temperature of the magnetic layer.

In some embodiments, a method includes forming a transistor on asubstrate; forming a source/drain contact landing on a source/drainstructure of the transistor; forming a dielectric layer over thesource/drain contact; etching the dielectric layer to form an openingexposing the source/drain contact; depositing a magnetic layer in theopening of the dielectric layer; depositing a first graphene layer overthe magnetic layer; depositing a filling metal to overfill a remainderof the opening of the dielectric layer, wherein the magnetic layer has agreater permeability coefficient than the filling metal; and performinga chemical mechanical polishing (CMP) process on the filling metal untilthe dielectric layer is exposed. In some embodiments, depositing thefirst graphene layer is performed by using an aromatic hydrocarbonprecursor with a radio frequency (RF) power turned on. In someembodiments, depositing the first graphene layer is performedsimultaneously with heating a temperature of the magnetic layer togreater than about 200° C. without using a heater. In some embodiments,the magnetic layer has a greater hysteresis coefficient than the fillingmetal. In some embodiments, the method further includes forming a linerin the opening of the dielectric layer prior to depositing the magneticlayer, wherein the magnetic layer has a greater permeability coefficientthan the liner. In some embodiments, the method further includes forminga second graphene layer over the filling metal, the first graphenelayer, and the magnetic layer, and not over the dielectric layer usingan aromatic hydrocarbon precursor with an RF power turned on. In someembodiments, the magnetic layer has a permeability coefficient greaterthan about 5×10⁻⁵ (H/m). In some embodiments, the magnetic layer has ahysteresis coefficient greater than about 300 (A/m).

In some embodiments, a structure includes a semiconductor substrate, agate structure, a source/drain structure, a contact, a dielectric layer,and a metal line. The gate structure is on the semiconductor substrate.The source/drain structure is adjacent to the gate structure. Thecontact lands on the source/drain structure. The dielectric layer spansthe contact and the gate structure. The metal line extends through thedielectric layer to the contact. The metal line comprises a liner overthe contact, a magnetic layer over the liner, a graphene layer over themagnetic layer, and a filling metal over the graphene layer. Themagnetic layer has a greater permeability coefficient than the fillingmetal. In some embodiments, the magnetic layer has a greater hysteresiscoefficient than the filling metal. In some embodiments, the magneticlayer has a greater permeability coefficient than the liner. In someembodiments, the magnetic layer has a greater thickness than thegraphene layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor structure, comprising: asemiconductor substrate; a gate structure on the semiconductorsubstrate; a source/drain structure adjacent to the gate structure; acontact landing on the source/drain structure; a dielectric layerspanning the contact and the gate structure; and a metal line extendingthrough the dielectric layer to the contact, the metal line comprising aliner over the contact, a magnetic layer over the liner, a graphenelayer over the magnetic layer, and a filling metal over the graphenelayer, the magnetic layer having a greater permeability coefficient thanthe filling metal.
 2. The semiconductor structure of claim 1, whereinthe magnetic layer has a greater hysteresis coefficient than the fillingmetal.
 3. The semiconductor structure of claim 1, wherein the magneticlayer has a hysteresis coefficient greater than about 300 A/m.
 4. Thesemiconductor structure of claim 1, wherein the magnetic layer comprisesat least one of cobalt, nickel, or iron.
 5. The semiconductor structureof claim 1, wherein the magnetic layer has a thicker thickness than theliner.
 6. The semiconductor structure of claim 1, wherein the magneticlayer has a thicker thickness than the graphene layer.
 7. Thesemiconductor structure of claim 1, wherein the graphene layer has athickness in a range from about 0.7 to 7 nm.
 8. A semiconductorstructure, comprising: a substrate; a gate pattern over the substrate;epitaxial structures over the substrate and at opposite sides of thegate pattern; a contact over one of the epitaxial structures; a firstmetal pattern over the contact, wherein when viewed in a cross section,the first metal pattern has a stepped sidewall structure having an uppersidewall, a lower sidewall laterally set back from the upper sidewall,and horizontal surface connecting the lower sidewall to the uppersidewall; and a first graphene layer lining the lower sidewall, uppersidewall, and the horizontal surface of the first metal pattern.
 9. Thesemiconductor structure of claim 8, further comprising: a magnetic layerover the first graphene layer.
 10. The semiconductor structure of claim9, wherein the magnetic layer has a greater permeability coefficientthan the first metal pattern.
 11. The semiconductor structure of claim9, wherein the magnetic layer has a permeability coefficient greaterthan about 5×10⁻⁵ H/m.
 12. The semiconductor structure of claim 8,further comprising: a second graphene layer over a top surface of thefirst metal pattern.
 13. The semiconductor structure of claim 12,further comprising: a second metal pattern over the first metal pattern;and a third graphene layer lining a sidewall and a bottom surface of thesecond metal pattern.
 14. The semiconductor structure of claim 13,further comprising: a magnetic layer formed on the third graphene layer,the magnetic layer separating the third graphene layer from the secondgraphene layer.
 15. A semiconductor structure, comprising: a substrate;a gate over the substrate; source/drain patterns over the substrate andat opposite sides of the gate; a source/drain contact over one of thesource/drain patterns; a first metal pattern over the source/draincontact; a first graphene layer lining a sidewall and a bottom surfaceof the first metal pattern; a first magnetic layer wrapping around thefirst graphene layer; and a second graphene layer lining a top surfaceof the first metal pattern.
 16. The semiconductor structure of claim 15,further comprising: a second metal pattern over the first metal pattern;and a third graphene layer lining a sidewall and a bottom surface of thesecond metal pattern.
 17. The semiconductor structure of claim 16,further comprising: a second magnetic layer wrapping around the thirdgraphene layer.
 18. The semiconductor structure of claim 17, furthercomprising: a fourth graphene layer lining a top surface of the secondmetal pattern.
 19. The semiconductor structure of claim 18, wherein thefourth graphene layer has a thicker thickness than the third graphenelayer.
 20. The semiconductor structure of claim 18, further comprising:an aluminum layer over the fourth graphene layer.